The chart below shows calendar year S&P 500 returns without dividends (grey vertical bars). Below the bars are red numbers which indicate the maximum intra-year drawdowns. The chart makes clear that 10% drawdowns are fairly common. What is not common is a drawdown of only 3% which was the case in 2017.

Another important observation from the above chart is that as long as the economy is not in a recession (areas shown with horizontal green bars), the calendar year returns are usually positive. The U.S. is not currently in a recession.

From January 1950 through December 2017, the S&P 500 has declined by 5-10% 41 times. The average length of the decline was one month. The average recovery from the low was one month. In the 11 cases that the S&P 500 declined by 10-20%, the sell-off lasted and average of 4 months and recovery took and average of 3 months.